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l_tofastrud

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Posts: 8
Reply with quote  #1 

I'm trying to measure a DSP loudspeaker management box.

 

Please look at the attachment to see what they look like.

 

I'm assuming that the errors are caused by timing issues when both the TEF25 and the DSP is set to 96kHz sampling.  It works better when the TEF is set to 48kHz but every now and then i see the same thing hapening then too.

 

Any way to avoid this?

 

Regards

Lars Tofastrud


Doug

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Posts: 71
Reply with quote  #2 
Hi Lars,
Im not sure I can explain the measurement, but it just might be art.....just curious if you have tried any other measurement systems on this ?

Doug

Ray

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Posts: 13
Reply with quote  #3 
Lars -

I too have never seen anything quite like this.  I doubt that "timing errors" should come into play since both the TEF and the DSP box are interfacing in the analog domain.

Have you listened to the output of the TEF while it is driving the DSP box?

Have you listened to the output of the DSP box while doing a measurement?

What you show should be clearly audible!

Have you tried testing the DSP with just a simple audio generator and AC voltmeter, and manually sweeping?  Such glitches should show up.

Do you see anything similar when testing anything else with the TEF?

I assume the interface in and out of the DSP is balanced analog audio.  Just to eliminate possible interface issues, have you tried placing a good transformer on the input and output of the DSP?

All modern audio A/D and D/A converters use oversampling with filtering in the digital domain.  Some converters allow choices of filters, and some may allow the filters to be disabled.  Running without the proper filters _could_ maybe explain the glitches, but I don't know how to explain the level shifts.

If you have a scope available, look at the output of the TEF and the output of the DSP while doing the test.  The problem should be clearly visible, and you should be able to tell if the outputs are clean sine waves or have ultrasonic trash on them.

I once tested a "digital wireless" system with converters the designers had made themselves, that had somewhat similar glitches except that the trigger was specific audio levels.  I doubt that any modern DSP designer would try something that stupid.

Let us know what you find!

Ray A. Rayburn
Ray@SoundFirst.com



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Ray A. Rayburn
Ray@SoundFirst.com

l_tofastrud

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Posts: 8
Reply with quote  #4 

Hey guys

 

I have found that it had nothing to do with the TEF at all.

 

It occurs only on my home PC and I have experienced USB speed issues on that before (the mother board also have lousy PCI speed) so I think USB on my motherboard is the problem.

 

Maybe I raised the red flag too early but there you go...

 

Thanks for your feedback!

 

Lars Tofastrud

Doug

Moderator
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Posts: 71
Reply with quote  #5 
Thanks Lars, for letting us know!  For once it isnt our fault!

Doug

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